This invention relates in general to electro-hydraulic control units for anti-lock brake systems and in particular to a method and apparatus for remote programming of a microprocessor in an Anti-lock Brake System electronic control module.
An anti-lock brake system (ABS) is often included as standard equipment on new vehicles. When actuated, the ABS is operative to control the operation of some or all of the vehicle wheel brakes. A typical ABS, which controls all four vehicle wheels, includes a plurality of normally open and normally closed solenoid valves which are mounted within a control valve body and connected to the vehicle hydraulic brake system. A separate hydraulic source, such as a motor driven pump, is included in the ABS for reapplying hydraulic pressure to the controlled wheel brakes during an ABS braking cycle. The pump is typically included within the control valve body while the pump motor is mounted upon the exterior of the control valve body.
It is also known to provide an ABS for the rear wheels only. Such a system is commonly referred to as a rear wheel anti-lock brake system (RWAL). Typically, RWAL does not include a motor driver pump, but utilizes the vehicle master brake cylinder as a source of pressurized brake fluid. While RWAL has a limited volume of pressurized brake fluid available during an ABS braking cycle, elimination of the pump and pump motor simplifies the system while reducing the cost thereof.
Both four wheel ABS and two wheel RWAL include an electronic control module which has a microprocessor. The control module is electrically coupled to the pump motor, for a four wheel ABS, a plurality of solenoid coils associated with the solenoid valves, one or more wheel speed sensors for monitoring the speed and deceleration of the controlled wheels and the vehicle brake light switch. The control module is typically mounted within a removable housing which is attached to the control valve body to form a compact unit which is often referred to as an ABS Electro-Hydraulic Control Unit (EHCU).
It is known to mount the coils for actuating the solenoid coils within the control module housing. Tubular sleeves which enclose the valve armatures extend from the valve body, forming a seal for the hydraulic brake circuit. When the control module housing is mounted upon the valve body, each of sleeves is received by an associated solenoid coil. Accordingly, the housing can be removed from the valve body for servicing of the electronics without opening the hydraulic brake circuit. The structure of the housing and coil assembly is commonly referred to as a Coil Integrated Module (CIM).
During vehicle operation, the microprocessor in the ABS control module continuously receives speed signals from the wheel speed sensors. The microprocessor monitors the wheel speed signals for potential wheel lock-up conditions and the brake light switch for brake acutuations. When the vehicle brakes are applied and the microprocessor senses an impending wheel lock-up condition, the microprocessor is operative to actuate the pump motor, in a four wheel ABS, and selectively operate the solenoid valves in the valve body to cyclically relieve and reapply hydraulic pressure to the controlled wheel brakes. The hydraulic pressure applied to the controlled wheel brakes is adjusted by the operation of the solenoid valves to limit wheel slippage to a safe level while continuing to produce adequate brake torque to decelerate the vehicle as desired by the driver.
The microprocessor includes a Read Only Memory (ROM) which is loaded with an ABS algorithm for controlling the operation of the microprocessor. The algorithm corresponds to a particular vehicle platform and can include trim values which are selected to match the characteristics of a specific configuration of the vehicle platform.